12Azobenzene-based bent-core liquid crystals demonstrate a variety of mesomorphic 13 behaviors and photochromic properties which are desirable for optical switching. Nowadays 14 azobenzene-based bent-core liquid crystal (ABLC) compounds usually exhibit at least one of the 15 following traits which are unfavorable for practical applications: (1) narrow temperature windows 16 of nematic phases, (2) high phase transition temperature, and (3) long period of light stimulation 17 to reach photostationary states. In this study, a series of ABLC compounds 4a-4g were synthesized 18 by adding azo functional groups and chlorine substituent to the central bent-cores to form 4-chloro-19 1,3-dizaophenylene bent-cores. These ABLC compounds were characterized by i. fourier-20 transform infrared spectroscopy (FTIR), 1 H and 13 C nuclear magnetic resonance (NMR), and mass 21 spectrometry (MS) for their structures, ii. differential scanning calorimetry (DSC) and polarized 22 optical microscopy (POM) for their mesogenic properties, and iii. ultraviolet-visible spectroscopy 23 (UV-Vis) and POM for their photosensitivity. The experimental results show that all compounds 24 exhibited broad temperature windows of mesogenic phases. In particular, compound 4c showed a 25 broad temperature window of 63.8 °C for nematic phase. Molecular simulations indicate that the 26 molecular dipole moments of compounds 4a-4g are closely associated with the temperatures of 27 Sm -N phase transition and temperature ranges of nematic phases. In addition, simulation results 28 reveal that the terminal alkyl chains exhibit a diphasic effect on the molecular polarity: extending 29 the terminal chain can initially reduce and then increase the molecular dipole moments due to the 30 severe structural disorder of overly extended terminal chain. These findings indicate that the 31 intermolecular forces play a vital role in shaping the mesogenic behavior of ABLCs. 32 Comprehensive characterizations of photochromatic properties show that 4c was highly 33 photosensitive and displayed rapid photoisomerization processes. At room temperature, compound 34 4c dissolved in ethyl acetate solution can reach photostationary state in 10 seconds. At 95 °C, 35 compound 4c in nematic phase became isotropic liquid under UV-irradiation in 3 seconds due to 36 the forward trans -cis photoisomerization and can be restored to be nematic under natural visible 37 light in 5 seconds because of the backward cis -trans photoisomerization. This study linking the 38 mechanistic details with mesogenic properties provides valuable insights to improve future design 39 of azobenzene bent-core liquid crystals for practical applications especially in photonic 40 applications. 41 42 Keywords: 43 bent-core liquid crystal; 4-chloro-1,3-diazobenzene; synthesis; nematic phase; photoisomerization; 44 molecular mechanics simulation. 45 46 65 alterations such as introducing different lateral substitutions on the bending core, 15,16,21 adjusting 66 the number of aromatic units, 17,22-24 modifying the type, ...

The photo-reversible isomerization property of the azo bend liquid crystal has become a hot topic in the research opt-electronic information materials, but its slow light response has become a key factor restricting its development. At present, the azo bond of the bent liquid crystal compound is far from the central nucleus, and the photo isomerization response time is long, mostly over minutes, which is not conducive to the application research of the photosensitive device. In this work, methyl-1,3-m-phenylenediamine was chosen the central nucleus. The azo bond is adjacent to both sides of the central ring and the terminal group is an alkyl chain. A series of novel curved bisazo benzene liquid crystal compounds were designed and synthesized, in order to shorten the light response time. The molecular structures of these compounds were identified by IR, 1 H NMR, 13 C NMR and ICP-MS spectroscopy. The phase transition temperature and phase texture of the liquid crystals were determined by differential scanning calorimeter (DSC) and polarized light microscopy (POM). The photo isomerization performance of 2-methyl-1,3-bis(4-((4-heptylphenyl)ester)-1-(E)-azophenyl)benzene (2c) was determined by UV-Vis absorption spectroscopy. The photo isomerism and response time of the liquid crystal compound and the doped nematic liquid crystal material were measured by UV-Vis spectrometer and polarizing microscope (POM). The experimental results show that all the curved bisazo benzene liquid crystal compounds designed and synthesized have the smectic phase and the phase temperature range is wide. The photo induced isomerization response time of compound 2c in the liquid crystal state of smectic phase and nematic phase is 2～3 s, and the recovery time of liquid crystal state in sunlight is 3～4 s, which can be reached in diluted ethyl acetate solution for 10 s. This type of bent bisazo liquid crystal compound has a relatively fast photo induced heterogeneous response speed.

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Azobenzene-based bent-core liquid crystals demonstrate a variety of mesomorphic behaviors and photochromic properties which are desirable for optical switching. In this study, a series of novel compounds were synthesized by adding azo functional groups and chlorine substituent to the central bent-cores to form a 4-chloro-1,3-dizaophenylene bent-core. Fouriertransform infrared spectroscopy (FTIR), 1 H and 13 C nuclear magnetic resonance (NMR), mass spectrometry (MS), differential scanning calorimetry (DSC), polarized optical microscopy (POM), and ultraviolet-visible spectroscopy (UV-Vis) were performed to evaluate the structure, mesogenic properties, and photosensitivity of these synthesized compounds. The experimental results show that these compounds exhibit a broad temperature window up to 63.8 °C for nematic phase. In addition, the enhancement of photonic properties of these compounds was exemplified by the high conversion ratio and the rapid rate of trans -cis photoisomerization of compound 4c. The cis fraction of 4c can reach 0.81. At 95 °C, 4c in nematic phase became isotropic liquid under UVirradiation in 3 seconds and can be restored to nematic under natural visible light in 5 seconds. At room temperature, 4c when dissolved in ethyl acetate solution can reach photostationary state in 10 seconds. Quantum mechanics modeling confirms that using azos instead of esters as the central linkages can effectively reduce the molecular dipole moment, which appears to promote favorable mesogenic behaviors and photonic characteristics. Moreover, varying the carbon number in the terminal alkyl chains can alter molecular dipole, especially the polarizability anisotropy, of which the variation is strongly correlated with the phase transition temperature and temperature range of nematic phase. These findings suggest that 1) changing azo group position can effectively alter the molecular dipole; 2) reducing molecular dipole interaction can promote favorable photonic properties of azobenzene bent-core liquid crystal. This study linking the mechanistic details with mesogenic behaviors provides a novel approach to improve the material design for photonic applications.